1. Field of the Invention
This present invention relates to a rapid test apparatus, more particularly to the rapid test apparatus in which the procedure comprising several times of injection of the same type reagent or injection of various types of reagents.
2. Description of Related Art
Take the sandwich ELISA for example. Capture antibody, antigen, detection antibody labeled with HRP, and chromogen solution are required to be loaded in sequence in this experiment. Because each step requires an incubation time and washing process, the overall sandwich ELISA often takes much time, even days, to accomplish the whole procedures. The conventional procedure using 96-wells microtiter plate must manually and repeatedly load the samples into the wells which not only wastes time but manpower.
In order to solve the problems stated above, Lee et al., in 2001, proposed microfluidic disc platform ELISA, abbreviated “CD-ELISA.” According to the testing procedures, the system utilizes rotational speed to control the reagents sequentially being released; therefore, the technologist just simply loads the reagents into each reservoir in advance, then the system will automatically carry out the reagent releasing and mixing processes.
The principle of CD-ELISA illustrates as follows: scribe multiple microfluidic channels on a microfluidic disc to form a number of reservoirs, and place microfluidic valves beneath those reservoirs. When the microfluidic disc rotates at a low speed, the liquid from the reservoirs to the entrance of the microfluidic valves will form a liquid-gas interface, and the pressure inside the liquid is also formed by centrifugation; besides, a capillary pressure obstructing the liquid from proceeding is generated by the surface tension on the liquid-gas interface. When the rotational speed increases, so does the liquid pressure, as the pressure is greater than capillary pressure, the liquid will break through the microfluidic valves and subsequently flow out of the reservoirs. On the contrary, the liquid is retained in the reservoirs if its pressure is less than capillary pressure.
Such design not merely simplifies the procedures but diminishes the volume of reagents required and broadens the reaction surface area. These improvements may accelerate the entire process, so that the overall detection time is shortened to 1 to 2 hours to complete.
However, in the execution of CD_ELISA, there are still some problems that need to be overcome. Suppose five kinds of reagents are required to be loaded in the process, and in each procedure, five microfluidic valves are needed. It is learned from references that for the sake of breaking through the microfluidic valves, each (burst) rotational speed, from the outer part of the microfluidic disc to the inner part, has to reach 327, 546, 968, 1180 and 1506 revolutions per minute (RPM) individually; nevertheless, due to the shape of the disc, there is no way to speed up the (burst) rotational speed to enlarge the gap. It seems like the releasing of reagents in sequence could be controlled by different rotational speed, but in reality, each (burst) rotational speed is not a constant value, instead, the value falls in the average of (burst) rotational speed plus or minus 20% within the range. Therefore, the foregoing fact influences the correctness of releasing the reagents in sequence. If the gap of the (burst) rotational speed between each microfluidic valve is not big enough, the range of each speed may overlap resulting in bursting more than one microfluidic valves at the same time under the same rotational speed, and this situation will lead the test to fail.
In the year of 2009, Cho et al. proposed using laser irradiated ferrowax microvalve to replace microfluidic valve as the device for obstructing the liquid from releasing. Use low melting-point wax to block the microvalves so that the reagents cannot burst the ferrowax microvalves but stay in the reservoirs. As the liquid should be released, laser will be applied to melt the wax to open the microvalves and release the liquid in sequence. Though the method can properly control when to burst the valves to avoid releasing the liquid in wrong order, it becomes more difficult to make the disc, in addition, a sophisticated machine is needed to perform the task, hence the cost of entire tests increases.
Without considering the huge cost, even if the ferrowax microvalves has solved the problem of unstable (burst) rotational speed of the microfluidic valve, during the test, a large quantity of liquid to be injected are still required. Suppose there are 12 sets of microfluidic channels on a microfluidic disc and 5 reservoirs within each set of the microfluidic channels, the reagents require to be injected in for 60 times. Again, it takes lots of time and manpower along with the volatilization problem. Considering the manufacture of products in the future, the fixed cost of making microfluidic discs must be amortized in order to achieve economic benefits via placing more sets of microfluidic channels on one disc. If 96 sets of microfluidic channels are arranged on a microfluidic disc and 5 reservoirs in each set of microfluidic channels, with each set of microfluidic channel to be loaded for 5 times, there are total 480 times for the reagents to be injected in the whole detection system. Thus it is sure time and labor consuming, and the man-made negligence error would be likely to rise.
“Flow splitting channels” might be a solution to the problems stated above; driven by the centrifugal force, the reagents only need to be injected once, and they will be automatically and evenly allocate to each reaction chamber. According to references, the principle of the flow splitting mechanism can be divided into two types. One is the serial flow splitting, designed as a serial arrangement of splitting chambers, and each exit of the splitting chambers is controlled by valves. The principle is that the liquid driven by centrifugal force or capillary force splits in sequence to fill each splitting chamber, and which is obstructed by the valves, then the excess liquid would be discharged to the waste chamber through the end of the flow splitting channel, so that each splitting chamber would fill with same volume of liquid, eventually, for the purpose of evenly allocating the liquid, the rotational speed would be speeded up for the liquid to break through the valves to the reaction chambers. In the year of 2005 and 2009, Anderson and Mark et al. proposed the serial flow splitting. In this manner, however, the liquid fills in sequence, and therefore takes longer time to split; moreover, the capillary force is easily unstable while filling up the splitting chambers, prone to failure of splitting.
The other type is the crotched flow splitting, its structure shapes as follows, a crotched flow channel is divided into two channels, and these two channels are further divided into four channels. The principle is that the liquid driven by centrifugal force flows into the crotched flow channels and it further divides into several branches flowing into the reaction chambers. Lee et al. in 2009 proposed combining CD_ELISA and the crotched flow channels; however, while the liquid splits, such design may easily be affected by the Coriolis force produced from the rotation of the disc, which makes the flow opposite to the direction of the flow channel as the disc rotates larger and causes the allocation of the liquid uneven. Although Lin et al. in 2010 proposed the effect of the Coriolis force could be reduced by amending the geometric shapes of the crotched flow channels to lower the rotational speed, the test result had demonstrated that in order to achieve the expected objective, the rotational speed should not exceed 1000 RPM. Once more, the problem has remained unsolved.